Apparatus for fusion bonding tubular recuperator structures

ABSTRACT

The novel embodiments disclosed herein also illustrate a novel method for making a recuperator structure. First and second pluralities of layers of elongated tubes are provided which are formed of a glass that is thermally crystallizable to a low expansion glass-ceramic. Each of the tubes is filled with a fluid medium that is expansible in response to the application of heat and the tubes have sealed ends to retain the expansible fluid medium entrapped therein. Each of the tubes has an essentially straight central portion and header connector portions continuing from each end of the central tube portions to the sealed end of the tube. The header connector tube portions of the first plurality of layers diverge away from the header connector tube portions of the second plurality of layers at the ends of the central tube portions when the first and second layers are placed on top of each other. The central tube portions of the first and second pluralities of layers are stacked one above the other with the axes thereof all essentially parallel and with the central tube portions of each first plurality layer in heat exchange relationship with the central tube portions of a second plurality layer. The header connector tube portions at each end of the central tube portions of each layer are arranged so that the header connector tube portions of the first layers diverge from the header connector tube portions of the second layers to provide four sets of separated header connector tube portion ends. Each set of header connector tube portion ends for one of the first and second pluralities of layers extend from the stacked array of tubes as a plurality of tube layers spaced apart by the central tube portions of the other of the first and second plurality of layers. The spaces between the layers and around the tubes adjacent the ends thereof of each set of header connector tube portions are filled with a header connecting material that is thermally crystallizable to a low expansion glass-ceramic which has substantially the same coefficient of lineal thermal expansion as the tubes to seal each set against fluid flow between the tubes. The outer surfaces of the assembly of tube layers and header connecting materials are constrained to prevent outward movement of the assembly. The constrained assembly is heat treated to soften the elongated tubes and enable the fluid medium therein to expand and urge the tubes into contact with adjacent tubes and with the header connecting material to fuse the assembly into an integral mass, and to effect crystallization of the tubes and the header connecting material into a low expansion glass-ceramic.

BACKGROUND OF THE INVENTION

This is a division of application Ser. No. 531,235 filed Dec. 10, 1975now U.S. Pat. No. 3,936,288 issued Feb. 3, 1976.

This application is a Division of my application Ser. No. 333,402, filedFeb. 16, 1973, now U.S. Pat. No. 3,926,251. This invention constitutesan improvement over the structure and method disclosed in my copendingpatent application Ser. No. 30,859, filed in the United States PatentOffice on Apr. 22, 1970 (now abandoned) and assigned to the assignee ofthe present invention, and an improvement over the structures andmethods disclosed in the patent application of Donald F. Mold and RonaldG. Rice also copending with the present application and also assigned tothe assignee of the present invention.

In the above-referenced copending application of mine, there isdisclosed an assembly or matrix of integrally fused tubes useful as acompact regenerative heat exchanger, buoyancy material, sound absorptionmaterial, heat insulation material, and the like. The advantages of thistype of structure and the requirements for each of the structures ofthis type, particularly a regenerator structure, are set forth fully inmy above-referenced application and need not be repeated here.

In that application, the regenerator structure consists of a pluralityof individual, axially parallel, open end glass-ceramic tubes which arethermally bonded to one another and integrated into an overallregenerator structure. Gas flow through the regenerator occurs throughthe individual tubes, one open end of each tube forming an inlet and theother open end of each tube forming the outlet. In a typical regeneratorinstallation, one or both faces of the regenerator is contacted by aseal bar. The regenerator matrix is rotated relative to the seal barwhich is urged against the regenerator end surface under an appreciableaxial load. Because of matrix end face-seal bar contact under thesealing load, some abrasive wearing of the matrix end face will occurover an extended service period, particularly since the matrix end faceis defined by the open ends of the individual tubes. Additionally, thestrength of the matrix and its ability to withstand axially or radiallyapplied loads in operation is dependent upon the degree of integralbonding between adjacent tubes. While such matrices made in accordancewith the disclosure in may copending application are capable offunctioning satisfactorily as regenerators, and although improvementshave been made in increasing resistance of the matrix end faces to wear,it is desirable to avoid the seal bar wear problems while retaining ahigh heat exchange efficiency. It is further desirable to do away withdrive connections, drive power, and rotating support required by aregenerator.

In my hereinabefore referenced application, there is also disclosed aheat exchange module which is constructed by superimposing a pluralityof layers of tubes, one layer above the other in successive parallelplanes, with the tubes in each plane being essentially parallel to eachother and transverse to the tubes in at least one of the adjacentlayers. The matrix of tubes, each of the tubes having both ends sealed,is heated to soften, expand and fuse the tubes together into an integralmodule. The sealed ends are opened and a plurality of such modules maybe assembled into a toroidally-shaped structure, each module beingseparated from an adjacent module by a wedge-shaped member.

In this latter module structure, the problem of seal bar wear has beenremoved. Although there is no movement of the module in this latterstructure, it is desirable to improve the heat exchange efficiency overthat provided by a crossflow relationship, while retaining theadvantages of an integral low expansion glass-ceramic structure of thetype described over the metal or ceramic heat exchange structures of theprior art.

A counterflow recuperator has one of the highest heat exchangeefficiencies known to the prior art. However, parallel and counterflowrecuperators, when made of metals such as nickle alloys, are expensiveand difficult to shape and braze. Such metal recuperators often leakafter repeated cycling. Recuperators have also been made of corrugatedsheets of ceramic which are stacked to form a crossflow and counterflowpatterns and then sintered. However, it is difficult to make the jointsof these prior art recuperators and failures usually occur in the jointareas. Heat-resistant materials used in the prior are recuperator bodiesare expensive and often fail in thermal fatigue, while sintered ceramicrecuperators may be undesirably porous.

In the above-referenced application of Mold and Rice a parallel andcounterflow recuperator structure has been disclosed which utilizesfirst and second pluralitites of layers of tubes with the axes of theintermediate portions of the tubes in each layer essentially parallel toeach other. A high heat exchange efficiency is achieved, but in theabove-noted structure one of the pluralities of layers is shorter thanthe other of the plurality of layers so that internal header connectionsmust be made to maintain two fluid streams separated. Such structureswill operate satisfactorily and achieve good heat exchange efficienciesbut may present fluid flow problems and assembly problems that aredifficult to overcome in high production applications.

Accordingly, it is an object of this invention to provide a recuperatorstructure and a method for making same wherein the structure hassuperior properties and utilizes a low expansion, nonporous heatexchange body such as made from glass-ceramic materials, and which doesnot have the deficiencies of the previous regenerator and recuperatorstructures.

It is another object of this invention to provide an improved method formaking a novel recuperator heat exchange assembly.

A still further object of this invention is to provide an improvedapparatus, and a method for making such apparatus, for conducting fluidsin heat exchange passageways which are substantially parallel to eachother and which keeps the fluid streams separated, thereby maintaining ahigh heat efficiency while providing a structure with separated headerconnection areas which are easily connected to the two fluid streamsbetween which heat is being exchanged. The structure does not requireany moving parts to function properly.

SUMMARY OF THE INVENTION

The above objects are illustrated in the several embodiments of thisinvention herein of recuperator heat exchange assemblies. Each finishedassembly includes a first plurality of layers of tubes, each tube in theplurality of layers having open ends and a portion intermediate the openends which is essentially parallel to corresponding intermediateportions of the other tubes in the same layer and to corresponding tubeportions in the other of said first plurality of layers to form a firstseries of longitudinally extending essentially parallel passageways forreceiving a first fluid.

A second plurality of layers of tubes, each tube in the second pluralityof layers having open ends and a portion intermediate the open endswhich is essentially parallel to corresponding intermediate portions ofthe other tubes in the same layer and to corresponding intermediate tubeportions in the other of the second plurality of layers, forms a secondseries of longitudinally extending essentially parallel passageways forreceiving a second fluid.

The intermediate tube portions of each of the first plurality of layersare disposed adjacent to, essentially parallel with, and in heatexchange relationship with the intermediate tube portions of at leastone of a second plurality of layers. The intermediate tube portions ofeach of the second plurality of layers are disposed adjacent to,essentially parallel with, and in heat exchange relationship withintermediate tube portions of at least one of the first plurality oflayers. There is thus formed a stacked array of tubes having four setsof open ends for receiving and discharging first and second fluids.

The portions of the tubes in each of one of the first and secondpluralities of layers between the intermediate portions thereof and afirst set of the open ends thereof extend obliquely with respect to theintermediate portions thereof to position the first set of open tubeends outside of the stacked array of tubes, thereby forming a firstplurality of obliquely extending tube portions having a first of saidfour sets of open ends outside of said stacked array and available forconnection to a first header means.

Another portion of each of the tubes in each of one of the first andsecond pluralities of layers between the intermediate portions thereofand a second set of the open ends thereof extend obliquely with respectto the intermediate portions thereof to position the second set of opentube ends outside of the stacked array of tubes, thereby forming asecond plurality of obliquely extending tube portions having a second ofsaid four sets of open ends outside of the stacked array and availablefor connection to a second header means.

The remaining tube portions of the tubes in the first and secondpluralities of layers between the intermediate portions thereof and thethird and fourth sets of the open ends thereof extend outwardly from theintermediate portions thereof to position the third and fourth sets ofopen ends away from the stacked array of contiguous intermediate tubeportions and away from each other to form the third and fourth sets ofopen ends available for connection to third and fourth header means.

Header connecting means are provided for each of the four sets of openends for receiving the open ends of each set and for closing the spacesbetween and around the open ends of each set to prevent leakage of thefluids from a header means between the tube ends of each set.

The tubes and the header connecting means are constructed of materialhaving essentially zero porosity, consisting essentially of an inorganiccrystalline oxide ceramic material, and having an average coefficient oflineal thermal expansion of about -18 to +50 × 10⁻ ⁷ /°C over the rangeof 0° - 300°C. The stacked layers of tubes and the header connectingmeans are fused together to form an integral assembly. While theintegral assembly described hereinbefore desirably has an averagecoefficient of lineal thermal expansion within the range set forthabove, the coefficient of lineal thermal expansion is advantageouslyabout -12 to +12 × 10⁻ ⁷ /°C over the range 0° - 300°C, and preferablyhas an average coefficient of lineal thermal expansion of about -5 to +5× 10⁻ ⁷ /°C over the range 0° - 300°C.

In a first embodiment disclosed herein the first plurality of tubes hasobliquely extending tube portions on each end of the intermediate tubeportions thereof. The second plurality of tubes in the first embodimentmay have essentially straight tube portions extending from each end ofthe intermediate tube portions. In the first embodiment of the inventionthe second plurality of tubes may also have obliquely extending tubeportions on each end of the intermediate tube portions.

In the embodiment illustrated first in the drawings, the oblique tubeportions of the first plurality of layers both extend obliquely awayfrom the intermediate tube portions thereof on the same side of the axesof the intermediate tube portions of the stacked array, while theoblique tube portions of the second plurality of layers both extendobliquely away from the intermediate tube portions thereof on theopposite side of the axes of the intermediate tube portions of thestacked array.

In yet another embodiment disclosed herein the first oblique tubeportions of the first plurality of layers on one end of the intermediatetube portions thereof extend obliquely away on one side of the axes ofthe intermediate tube portions while the second oblique tube portions ofthe first plurality of layers on the other end of the intermediate tubeportions thereof extend obliquely away on the other side of the axes ofthe intermediate tube portions. The first oblique tube portions of thesecond plurality of layers on one end of the intermediate tube portionsthereof extend obliquely away from the axes of the intermediate tubeportions at the same end of and in an opposite direction away from theaxes as does the first oblique portion of the first plurality of layers.The second oblique tube portions of the second plurality of layers onthe other end of the intermediate tube portions thereof extend obliquelyaway from the axes of the intermediate tube portions at the same end ofand in an opposite direction away from the axes as the second obliqueportion of the first plurality of layers.

In still another embodiment of the invention herein the first pluralityof tubes has obliquely extending tube portions at one end of theintermediate tube portions thereof and essentially straight headerconnecting tube extending portions at the other end of the intermediatetube portions thereof. The second plurality of tubes has obliquelyextending tube portions at one end of the intermediate tube portionsthereof and essentially straight extending header connecting tubeportions at the other end of the intermediate tube portions thereof. Theobliquely extending tube portions of the first and second plurality oflayers are disposed at opposite ends of the stacked array.

The header connecting means may comprise a foamed ceramic cement moldedand heat treated in place around the tubes adjacent the open endsthereof of each of the four sets of open ends of the first and secondpluralities of layers of tubes.

Each of the sets of tube ends may extend from the array in the form of aplurality of tube layers having spaces formed therebetween where theintermediate tube portions for one of the first and second layers oftubes of the stacked array space apart the intermediate tube portions ofthe other of the first and second layers of tubes. The header connectingmeans may then include a foamed ceramic cement molded and heat treatedin place in the spaces between the plurality of layers of tubes andaround the tubes adjacent the open ends thereof of each of the sets ofopen tube ends, to provide a closure around each set of open tube endswhich has essentially zero porosity, has substantially the samecoefficient of lineal thermal expansion as the tubes, and which fusestogether with the tubes around the open ends thereof to provide anintegral connecting means for a header for delivering fluid to orreceiving fluid from the set of open ends.

An alternative header connecting structure for each of the sets of opentube ends may include a plurality of tightly packed individually axiallyelongated elements arranged with their axes parallel to each other andin layers in the spaces between the tube end layers, and sealant meansinterposed in the interstices between header elements, between tubeends, and between layers of header elements and tube ends to provide anintegral connecting means. The sealant means may be a ceramic cement, afoamed ceramic cement, a sintered frit, or other suitable sealant whichaccomplishes the objectives set forth herein. Advantageously, each layerof header elements includes at least one axially elongated tube havingrelatively thin walls and sealed ends, each such tube having beenexpanded by heat treatment to compress the sealant material to insureclosing the interstices between header elements and the tube endportions of the tubes in adjacent layers.

Other objects, features and advantages will become apparent from thefollowing description when taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view in perspective of an embodiment of a recuperatorstructure assembly illustrating the teachings of this invention;

FIGS. 2 and 3 are plan views of the different types of layers of tubesutilized in the structure illustrated in FIG. 1;

FIG. 4 is a cross-sectional view of the assembly illustrated in FIG. 1placed in a mold for heat treatment;

FIG. 5 is a cross-sectional view of the apparatus illustrated in FIG. 4taken along lines V--V of FIG. 4;

FIG. 6 is a cross-sectional view of a portion of the intermediate tubeportions of a first embodiment of this invention before heat treatment;

FIG. 7 is a cross-sectional view of the sections illustrated in FIG. 6showing the expansion of the tube after heat treatment;

FIG. 8 is a cross-sectional view of the intermediate tube portions of asecond embodiment of the teachings of this invention taken before heattreatment of the assembly;

FIG. 9 is a cross-sectional view of the section illustrated in FIG. 8taken after heat treatment has been applied thereto;

FIG. 10 is a plan view of apparatus for preparing pluralities of layersof tubing used in making the novel recuperator structures of thisinvention;

FIG. 11 is a side elevational view of the apparatus illustrated in FIG.10;

FIG. 12 is a cross-sectional view of a portion of the apparatusillustrated in FIG. 11 taken along lines XII--XII of FIG. 11;

FIG. 12a is a cross-sectional view of the apparatus shown in FIG. 12illustrating an alternative tube bending apparatus and method;

FIG. 13 is a view in perspective of a second embodiment of the teachingsof this invention;

FIG. 14 is a schematic representation of a portion of the assemblyillustrated in FIG. 13;

FIG. 15 is a schematic representation of an alternate embodiment for theapparatus illustrated in FIG. 13; and

FIGS. 16, 17 and 18 schematically illustrate third, fourth, and fifthalternate embodiments of the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 3, there is illustrated a recuperator heatexchange assembly 20 which embodies the teachings of this invention. Theassembly 20 includes a first plurality of layers or groups 30 of tubes32. Each tube 32 in the plurality of layers 30 has open ends 39 and aportion 34 intermediate the open ends 39 which is essentially parallelto corresponding intermediate portions 34 of the other tubes 32 in thesame layer and corresponding intermediate tube portions 34 in the otherof the first plurality of layers 30 to form a first series oflongitudinally extending essentially parallel passageways for receivinga first fluid.

A second plurality of layers or groups 40 of tubes 42 are interposedbetween the first plurality of layers of tubes 30. Each tube 42 in thesecond plurality of layers 40 has open ends 49 and a portion 44intermediate the open ends 49 which is essentially parallel tocorresponding intermediate portions 44 of the other tubes 42 in the samelayer and the corresponding intermediate tube portions 44 in the otherof the second plurality of layers 40 to form a second series oflongitudinally extending essentially parallel passageways for receivinga second fluid.

The intermediate tube portions 34 of each of the first plurality oflayer 30 are disposed adjacent to, essentially parallel with, and inheat exchange relationship with the intermediate tube portions 44 of atleast one of the second plurality of layers 40. The intermediate tubeportions 44 of each of the second plurality of layers are disposedadjacent to, essentially parallel with, and in heat exchangerelationship with the intermediate tube portions 34 of at least one ofthe first plurality of layers 30. There is thus formed a stacked arrayof tubes which has four sets of open ends for receiving and dischargingfirst and second fluids.

The portions 36 of the tubes in each of one of the first and secondplurality of layers (such as layer 30) between the intermediate portionsthereof 34 and a first set of the open ends 39 thereof, extend obliquelywith respect to the intermediate portions 34 thereof to position thefirst set of open tube ends 39 outside of the stacked array of tubes,thereby forming a first plurality of obliquely extending tube portionshaving a first of the four sets of open ends outside of the stackedarray and available for connection to a first header means.

Another portion 38 of each of the tubes 32 in each of one of the firstand second pluralities of layers (in this instance the layers 30)between the intermediate portions 34 thereof and a second set of theopen ends 39 thereof, extends obliquely with respect to the intermediateportions 34 thereof to position the second set of open tube ends outsideof the stacked array of tubes, thereby forming a second plurality ofobliquely extending tube portions 38 having a second of the four sets ofopen ends outside of the stacked array and available for connection to asecond header means.

The remaining tube portions 46, 48 of the tubes 42 in the first andsecond pluralities of layers (in this instance the plurality of layers40) between the intermediate portions 44 thereof and the third andfourth sets of open ends 49 extend outwardly from the intermediateportions 44 to position the third and fourth sets of open ends 49 awayfrom the stacked array of contiguous intermediate tube portions 34, 44and away from each other and the other sets of open ends to form thethird and fourth sets of open ends available for connection to third andfourth header means.

In the embodiment illustrated in FIG. 1 the oblique tube portions 36, 38of the first plurality of layers 30 both extend obliquely away from theintermediate tube portions 34 thereof on the same side of the axes ofthe intermediate tube portions 34, 44 of the stacked array, while theoblique tube portions 46, 48 of the second plurality of layers 40 bothextend obliquely away from the intermediate tube portions 44 thereof onthe opposite side of the axes of the intermediate tube portions 34, 44of the stacked array.

Each of the sets of oblique tube end portions extend from the array inthe form of a plurality of tube layers having spaces 50 formedtherebetween where the intermediate tube portions of one of the firstand second layers 30, 40 of tubes 32, 42 of the stacked array spaceapart the intermediate tube portions 34, 44 of the other of the firstand second layers of tubes 30, 40.

Header connecting means 52 are provided for the assembly in FIG. 1 andin this embodiment includes a foamed ceramic cement molded and heattreated in place in the spaces 50 between the plurality of layers oftubes and around the tubes adjacent the open ends 39, 49 thereof of eachof the sets of open tube ends, to provide a closure around each set ofopen tube ends which has essentially zero porosity, has substantiallythe same coefficient of lineal thermal expansion as the tubes, and fusestogether with the tubes around the open ends thereof to provide anintegral connecting means for a header for delivering fluid to orreceiving fluid from the set of open ends.

Although not shown herein, it is to be understood that additional layersof tubes or glass rods may be utilized on the outside surfaces of theassembly 20 of FIG. 1 to provide insulation and protective skins for theassembly. Such insulation and protective skins of rods and tubes arefully disclosed in the copending application of Mold and Rice which isreferenced hereinbefore.

The tubes 32, 42 and the header connecting means 52 are formed frommaterial having essentially zero porosity, consisting essentially of aninorganic crystalline oxide ceramic material, and having an averagecoefficient of lineal thermal expansion of about -18 to +50 × 10⁻ ⁷ /°Cover the range of 0° - 300°C. The stacked layers of tubes 32, 42 and theheader connecting means 52 are fused together to form an integralassembly as illustrated at 20.

As noted above, while the assembly desirably has an average coefficientof lineal thermal expansion within the range just set forth, thecoefficient of lineal thermal expansion is advantageously about -12 to+12 × 10⁻ ⁷ /°C over the range 0° - 300°C, and preferably has an averagecoefficient of lineal thermal expansion of about -5 to +5 × 10⁻ ⁷ /°Cover the range of 0° - 300°C.

A ceramic cement and foamable ceramic cement suitable for use inmanufacturing the assembly of FIG. 1 and the structures illustratedhereinafter is disclosed in U.S. Pat. No. 3,189,512, issued June 15,1965, and in U.S. Pat. No. 3,634,111, issued Jan. 11, 1972. Usuallyround thermally crystallizable tubing is used in forming the structureof the invention, the drawing of round glass tubing to controlleddimensions being an old established art in the industry.

Referring to FIGS. 4 through 11 there is illustrated apparatus for and amethod of making the assemblies illustrated herein. Referring first toFIGS. 10, 11, and 12 there is illustrated apparatus for forming thelayers of tubes to be utilized. To facilitate the assembly of the tubes72 in FIGS. 10 through 12 so that the layers may be superimposed oneupon another, a plurality of straight tubes 72 with open ends which havebeen precut to a specified length are fed into a hopper 80 by means notshown. The hopper 80 may be continuously vibrated by means of a vibrator82 in contact therewith, so that the tubes are maintained in parallelrelationship and are deposited individually through the hopper opening84 at the base of the hopper 80 onto a forming conveyor 120 disposeddirectly beneath the opening 84 and continuously moving in a directionaway from the hopper 80.

A tube dispensing mechanism is indicated generally at 90 and is utilizedto periodically permit the exit from the hopper opening 84 of apredetermined number of tubes 72 in succession to form separate layers74. The mechanism 90 includes a hopper gate 92 having a sharp bottomedge 94 which enables separation of successively issuing tubes. Thesharp bottom edge may be made of hard rubber or other suitable materialwhich will not damage the tubes as they are separated as each groupexits from the hopper opening 84. The hopper gate 92 is mounted to bereciprocated vertically in gate slides 96. A motor 100 rotates areciprocating wheel 102 which has a wheel stud 104 offset from thecenter thereof. The wheel stud 104 extends through a slot 106 formed ina connector bar 108. The connector bar 108 extends downwardly to thehopper gate 92 and has a second connector bar slot 110 formedtherethrough. A gate slide stud 112 extends from the gate 92 through theslot 110. In operation, as the motor 100 rotates the wheel 102, the studbar 104 is raised and lowered with respect to the connector bar 108 andthe gate slide 92. The slots 106 and 110 are formed in the connector bar108 so that the relative reciprocation of the studs 104, 112 enables thelifting of the gate 92 for a predetermined interval and the lowering ofthe gate for a second predetermined interval. A predetermined number oftubes 72 may exit from the hopper 80 after the gate is raised and beforethe gate is again lowered to provide separation of the issuing tubes 72into layers 74 on the conveyer 120. The rate of movement of the conveyor120 and the rate of deposit of the tubes 72 thereon are adjusted so thatthe tubes 72 are deposited and maintained in parallel, contactingrelationship with adjacent tubes in each layer 74. As the conveyor 120and each layer 74 moves away from the hopper 80 an overhead conveyor 130contacts the layers 74 and holds them together and firmly on theconveyor 120 to retain the layers 74 in place while operations areperformed thereon.

As the layers 74 move away from the hopper 80 the ends of the tubes 72in each layer pass through flames from oppositely disposed ribbonburners 140 mounted on either side of the conveyor belt 120. The flamesof the burners 140 fuse and close the tubes to trap air within thetubes. The flames from the burners 140 are directed so they do notadversely affect any other portion of the tube 72 in the layer 74, butonly impinge on the tube ends.

As the layers 74 of tubes continue along the conveyor 120, a second setof ribbon burners 150 is directed downwardly at an angle toward the endsof the intermediate or central straight parallel portions of the tubes72. As the layers 74 pass by the ribbon burners 150 the glass tubesreceive heat at the desired point of blending. As the glass in each tubesoftens, the weight of the cantilevered portion of the tubing 72 bendsthe tubing to a desired angle as provided by the trapezoidalcross-section of the belt 122 of the conveyor 120. This is illustratedin FIG. 12 wherein the solid line configuration of the layer 74represents the layer as it is entering the area between the oppositelydisposed burners 150, while the dotted line portion of the layers 74indicates the obliquely extending position that the tube end portionshave assumed in response to having the portion at the ends of thecentral parallel parts of the tube softened by the heat from the burners150.

It has been found that under certain circumstances the method of tubebending does not always function satisfactorily. That is, for certaintube diameters, glass compositions, and the weight and lengths of tubeportions that are cantilevered, the tube portions will either not bendin response to gravitational forces and/or the heat applied to obtain agravitational bend may be excessive and cause a sealing of or a reducedsize in the internal passageway of a tube at the bend.

Therefore, alternate bending method and apparatus are illustrated inFIG. 12a. Although the ribbon burners 150 are not shown in FIG. 12a, itis assumed that the tube layers 74 have already passed beneath theburners 150 and have received enough heat at the bending areas of thetubes to soften the bending areas.

The layers 74 then pass below a pair of oppositely disposed bending cammeans 124. The cam means 124 are cam wheels rotatably driven on offsetshafts 126. The speed of rotation of the cams 124 is such that the tubeengaging portions of the cams 124 are rotated out of the way to allowthe straight ends of the tubes of a layer 74 to be moved into positionbetween the oppositely disposed cams 124. The cams 124 then rotate inthe direction of the arrows to move downwardly into contact with thecantilevered portion of the tube ends of the layers 74 and bend theheated tubes to the position shown in FIG. 12a.

It is obvious that the conveyor flight 122 and/or the cams 124 may beindexable or have continuous movement to produce the desired results.The apparatus illustrated in FIG. 12a may be positioned between theburners 150 and the end of the upper flight 122 of the conveyor 120.

After the tube ends are bent to the desired angle the layers 74 aredischarged from the conveyor 120 down a guide slide plate 160. The widthof the plate 160 may be such so that the intermediate or centralportions of the tubes 72 are retained in alignment. As each layer oftubes reaches a flattening or layer-shaping conveyor 170, the downwardlydepending tube ends contact the upper flight of the conveyor 170 and aremoved forwardly with respect to the intermediate tube portions thereofso that the tube layers assume the configuration illustrated in FIG. 10on conveyor 170.

A thin layer of air-setting bonding material may be sprayed on the uppersurface of the layers 74 on the conveyor 170 by means of a nozzle 180 ofa spray gun, which material bends the tubes together so that the layersof tube become rigid enough to be handled like a thin sheet of plasticmaterial. For example, a urethane compound such as Spraylat No. 6210 maybe used.

Referring now to FIGS. 4 and 5 there is illustrated a constraining moldindicated generaly at 60. The mold 60 includes a bottom wall portion 62,side walls 64, end walls 66, and a heavy top cover wall 68. Perforations69 may be formed in the top cover 68 and the bottom wall 62 to permitthe escape of gas from between the interstices of the tubing as theassembly is heat treated.

The layers of tubing 74 as produced by the apparatus illustrated inFIGS. 10 through 12 may be utilized to form the assembly 20 illustratedin FIG. 1 by stacking a first layer 74 in the mold 60, then an invertedlayer 74, and proceeding in this manner to provide the first and secondplurality of layers 30, 40. The tubes in the layers are tightly packedin the mold 60 and the spaces 50 filled with a foamable ceramic cementmaterial 52 as described hereinbefore. The end walls 66 may then be putinto place and the top cover 68 placed on top of the assembly 20. Theouter surfaces of the assembly 20 are then constrained or restrictedagainst movement in a direction outwardly from the assembly.

The mold 60 with the assembly therein is then placed in a furnace andsubjected to a heat sufficient to soften the glass walls of the sealedend tubes to cause the walls of sealed end tubes to bloat or expand inresponse to the heating of the expansible fluid medium in each tube sothat adjoining contacting wall surfaces within the layers and betweenthe layers are fused together and so that the foamable ceramic cementmaterial 52 is activated to completely fill the interstices between thetubes between the spaces 50 and around the ends of the tubes to form aunitary assembly 20. As the individual tubes expand, the air or othergases in the interstices may exit through the perforations 69 which areformed in the restraining top and bottom walls 68, 62 of the mold 60.

The heating of the thin-walled sealed end tubes expands them into closecontact with each other, and into the interstices between the tubes andbetween the layers of the sealed end tubes to a greater or lesserextent, ideally to an extent to substantially fill the interstices.Referring to FIGS. 6 and 7 a cross-sectional view of the intermediateportions of the tube layers 30 and 40 is illustrated in which the axesof each intermediate tube portion in each layer each lie in a planeformed by the lines of contact between adjacent tubes. That is, thetubes are directly one above the other.

Referring to FIG. 7 there is illustrated a cross-section of the portionillustrated in FIG. 6, after heat treatment, in which the tube wallshave been expanded to substantially fill the interstices. In thisinstance the resulting bloated tubes become essentially square orrectangular in cross-section.

The glass tubes are fusing to each other and with the foamable ceramicmaterial 52 and are also undergoing nucleation during the heattreatment, and heating of the assembly is continued for a timesufficient to in situ crystallize the glass to an at least partiallycrystalline material, commonly referred to as a glass-ceramic.

After the assembly has been crystallized, and usually after cooling toroom temperature, the assembly 20 may be removed from the mold 60 andthe tube ends removed by grinding, by diamond saw, or other suitablemethods to obtain the opened ends 39, 49 as illustrated in FIG. 1.

Well suited for use in the methods of this invention are thermallycrystallizable glasses that are convertible by heating to glass-ceramicbodies. As used herein, a glass-ceramic is an inorganic, essentiallycrystalline oxide ceramic material derived from an amorphous inorganicglass by in situ bulk thermal crystallization.

Prior to thermal in situ bulk crystallization, thermally crystallizableglasses can be drawn into tubing using conventional glass-formingtechniques and equipment. Similarly, the thermally crystallizableglasses may be made into various ceramic cements suitable for use as thematerial 52 and as disclosed in the U.S. Pat. No. 3,189,512 and No.3,634,111 referenced hereinbefore.

After being assembled in the manner shown in FIGS. 4 and 5, thethermally crystallizable glass tubes and ceramic cement material aresubjected to a controlled heat treatment until the sealed end tubes havebeen expanded, the foamable ceramic cement activated, the assemblyportions have been fusion sealed to each other and crystallization ofthe entire structure has been effected.

Thermally crystallizable glass compositions and the glass-ceramicsresulting from thermal in situ crystallization thereof which are usefulin the method and product of this invention are those which have, in thecrystallized state, a coefficient of thermal expansion in the range offrom -18 to +50 × 10⁻ ⁷ /°C over the range 0° - 300°C and preferably aslow as -12 to +12, or -5 to +5, × 10⁻ ⁷ /°C over the range 0° - 300°C.The compositions usually used are those containing lithia, alumina, andsilica, together with one or more nucleating agents including TiO₂,ZrO₂, SnO₂ or other known nucleating agents. In general, suchcompositions containing in weight percent about 55 to 75 SiO₂, about 15to 25 Al₂ O₃ and about 2 to 6 Li₂ O, together with about 1.5 to 4 weightpercent of nucleating agents selected from one or more of TiO₂, ZrO₂ andSnO₂, can be employed. Preferably, not more than about 2.5 weightpercent TiO.sub. 2 is usually used or the crystallization is undesirablyrapid to be compatible with the fullest expansion of the tubes in thebloating process.

Other ingredients can be present in small amounts, as is understood inthe art, such as even as much as four or five weight percent ZnO, up toas much as three or four weight percent CaO, up to as much as eightpercent MgO, and up to as much as five percent BaO, as long as thesilica plus alumina plus lithia and the nucleating agent(s) are at leastabout 85, usually 90, weight percent of the total glass and the glasscomposition will thermally crystallize to a glass-ceramic having thedesired low expansion coefficient set forth hereinbefore. Exemplarycompositions which can be used in the process of the invention includethose compositions disclosed in U.S. Pat. No. 3,380,818; thosecompositions disclosed in U.S. Ser. No. 464,147 filed June 15, 1965, nowabandoned; and corresponding British Pat. Nos. 1,124,001 and 1,124,002dated Dec. 9, 1968; and also those compositions disclosed in U.S.application Ser. No. 866,168 filed Oct. 13, 1969, which issued as Pat.No. 3,625,718 on Dec. 7, 1971, and corresponding Netherlands PrintedPat. Application No. 6805259; and also those compositions set forth inU.S. application Ser. No. 146,664 filed May 25, 1971, now abandoned.

In any event, the thermally crystallizable glass tubing, glass rods ifused as discussed hereinafter, and the sealant materials in thelithia-alumina-silica field containing nucleating agents as beforedescribed, are assembled as previously set forth and the constrainedassembly of sealed tubing (containing the heat-expansible fluid) and theheader connecting and sealing material 52 are heated at any suitablerate that will not thermally shock the assembly up to a temperaturerange in the maximum nucleating range of the glass. The maximumnucleation range can be determined for all such glasses by the generalmethod outlined in the above-referenced U.S. Pat. No. 3,380,818,beginning at Column 9, line 54.

For the process of the present invention, where expansion and fusion areto be effected or initiated while nucleation is occurring, it ispreferred that the assembled tubes be heated in the range of 50°F to250°F above the annealing point for a period of one hour or more. Thistime can be extended to 10 or 20 hours, and even longer times are notharmful. During this time of heating in such temperature range,nucleation is effected as well as fusion aided by pressure exerted byexpansion of the trapped fluid in the sealed end tubes. Thereafter, thetemperature is raised to a higher temperature than the first heatingrange, which higher temperature is at least 200°F above the annealingpoint temperature or may be as high as the final crystallizationtemperature (usually 1800° to 2300°F). The final crystallization can beeffected at any such temperature range higher than thenucleation-expansion-fusion temperature (50° to 250°F above theannealing point temperature) and can be as low as 200°F above theannealing point or as high as 2300°F or as high as the upper liquidustemperature.

In this second stage of heating further expansion and the beginning ofcrystallization is effected, followed by the completion ofcrystallization on continued heating to a degree such that the assemblyhas an average coefficient of expansion in the range set forthhereinbefore.

While the temperature may be raised directly to the finalcrystallization temperature range at a suitable furnace heating rate,usually in the range of 10° to 300°F per hour, it is usually preferredto allow crystallization to be effected slowly while further expansionof the sealed end tubes and the fusion of sealed end tubes and rods, ifused, and the header connecting material is being effected by having anintermediate step between the first nucleation-and-fusion temperaturerange and the final crystallization temperature, which range is usuallyabout 200°F to about 700°F usually from 200° to 500°F, above theannealing point of the original glass. Exemplary holding times in thisintermediate range are from 1 to 8 hours, after which the assembly isheated up to the final crystallization temperature, usually in the rangefrom about 1800° to 2300°F.

Obviously, no specific heat treatment instructions can be given suitablefor all thermally crystallizable glass compositions. As is well-known,glass-ceramics do not have adequate strength if they are notsufficiently nucleated before crystals are allowed to grow appreciablein size, so that routine experiments known to those skilled in the artare used to determine what length of time is best to obtain an adequatenumber of crystallization centers or nuclei in the glass in thenucleation temperature range of 50° to 250°F above the annealing point.

Another point that must be kept in mind is that, if it is an object toobtain appreciable expansion beyond that necessary to get good fusionbetween the tubes, in other words to get appreciable reshaping of thesealed end tubes to fill the interstices between tubing, one should notraise the temperature too slowly when going from a nucleationtemperature range to the intermediate range, since a rigid crystallinenetwork may begin to set in and to prevent further expansion. It isfound that some compositions can be heated at a rate as low as 10° to50°F per hour to this intermediate temperature range and still getsufficient expansion of the tubing. On the other hand, some compositionshave been found not to fully expand unless the heating rate from theinitial nucleation-fusion temperature range to the intermediatetemperature range is used, sometimes on the order of at least 200°F to300°F per hour or higher.

The length of time of heating in the final crystallization temperaturerange of 1800°F to about 2300°F is from one-half hour to five or sixhours, although longer times normally are in no way deleterous. Afterthe crystallization has been completed, the structure can be cooled atfurnace rate or, dependent upon its expansion characteristics, in airbecause the structure is of such low expansion that thermal shock willnot harm it.

After the heat treatment just described, the product can now be cooledand the sealed ends of the tubes in the layers 30 and 40 cut or groundaway to open each tube to atmospheric pressure. Alternatively, if theintermediate step of crystallization heat treating at a temperaturerange of 200° to 700°F above the annealing point temperature is used,the heat treatment can be interrupted after this intermediate step andcooled somewhat or even cooled to room temperature, and the ends of thetubes in the layers 30, 40 cut or ground away and opened to atmosphericpressure. Then the assembly can be heated up again into the finalcrystallization heat treatment range, where further and finalcrystallization is effected.

Referring now to FIG. 13, there is illustrated a second embodiment ofthe teachings of this invention in which an assembly generally indicatedat 20a, again has first and second pluralities of layers of tubes 30a,40a stacked on top of each other. In this instance the intermediate orcentral tube portions 34a, 44a of the tubes 32a, 42a are againessentially straight, essentially parallel to the other central tubeportions in the same layer and to the central tube portions in the otherlayers. However, the header connecting tube portions are formed somewhatdifferently. In the layers 30a the header connecting tube portions 36aextend obliquely with respect to the axes of the intermediate tubeportions 34a, 44a so that the first set of open ends 39a are disposed oroffset to one side of the assembly 20a. The other header connecting tubeportions 38a of the tubes 32a, however, extend directly straight andoutwardly from the ends of the stacked array of intermediate portions34a, 44a until the open ends 39a thereof are separated from the rest ofthe body or assembly.

Correspondingly, the header connecting tube portions 48a of the layers40a extend obliquely with respect to the axes of the intermediate tubeportions 34a and 44a so that the tube openings 49a are offset to theside and away from the tube openings 39a of the header connector tubeportions 38a. The other header connector tube portions 46a of the layers40a are extended straight out from the ends of the stacked array ofintermediate tube portions 34a, 44a for a distance sufficient to placethe open ends 49a past and away from the set of open ends 39a of theheader connector tube portions 46a.

Thus, the first plurality of tubes 30a has obliquely extending tubeportions 36a at one end of the intermediate tube portions 34a thereofand essentially straight extending tube portions 38a at the other endintermediate tube portions 34a thereof. The second plurality of tubes42a has obliquely extending tube portions 48a at one end of theintermediate tube portions 44a thereof and essentially straightextending tube portions 46a at the other end of the intermediate tubeportions 44a thereof. The obliquely extending tube portions 36a and 48aof the first and second plurality of layers 30a, 40a are disposed atopposite ends of the stacked array.

Thus, four sets of open ends are again provided in separated positionsfor easily connecting header means thereto for directing two separatefluid streams into the intermediate portions 34a, 44a to obtain a heatexchange therebetween.

An alternative embodiment of header connecting means 52a is illustratedin the spaces 50a formed between the extending header connector tubeportion layers of the assembly 20a in FIG. 13. As best shown in FIG. 14,the header connecting means 52a may comprise a plurality of tightlypacked individually axially elongated elements 54 arranged with theiraxes parallel to each other and disposed in layers between the headerconnecting tube portion layers, such as 36a. Sealant material 56 isinterposed between the adjacent elements 54 and between the tube layers36a (or 38a, 46a, 48a) and around the header connector tube portions andheader connector elements to join the elements into an integral masswhich is nonporous and prevents a fluid from a header connecting meansfrom flowing between the interstices of the header connecting tubeportions. The sealant material 56 may be a ceramic cement or a foamableceramic cement such as described in the hereinbefore referenced U.S.Pat. Nos. 3,189,512 and No. 3,634,111. The sealant material 56 may alsobe a sinterable frit, the use and disposition of a sinterable fritmaterial to close interstices between tubes or rods being disclosed inthe copending application Ser. No. 169,216, filed Aug. 5, 1971, now U.S.Pat. No. 3,773,484, by Marion I. Gray, Jr. and assigned to the sameassignee as the assignee of the present invention.

In a manner fully described in the above-referenced appliation Ser. No.169,216, now U.S. Pat. No. 3,773,484, each of the glass rods, or of theglass tubes to be described hereinafter, utilized in the manufacture ofthe header connecting means 52a receives a coating of a sinterablethermally crystallizable frit. The entire exterior surfaces of thesetubes or rods are preferably coated with a frit composition identifiedin the above-referenced application Ser. No. 169,216, (U.S. Pat. No.3,773,484) the frit composition preferably being of the same thermallycrystallizable glass composition of which the tubes and rods are formed.

It is advantageous to include at least one individually axiallyelongated tube with sealed ends and expansible fluid medium entrappedtherein in the layers of the header connecting material 52a. It is mostadvantageous, if a sinterable frit sealant material 56 is beingutilized, to utilize sealed glass tubes as shown at 54a in FIG. 15 forthe entire layers of header connecting means 52a. Thus, during the heattreating of the assembly 20a and during the bloating or expanding of thetubes 32a, 42a and of the tubes in the header connecting means 52a andthe fusion of the tube wall surfaces, and interspersed rods if utilized,into the unitary assembly, the finely divided frit will sinter anddistribute itself in the interstices between the tube walls (and betweenthe tube walls and rods if utilized) to aid in securing and fusing thewalls and/or rods to one another.

The frit interposed in the interstices between the expanding tubes maybe subjected to substantial pressures generated by the expansion of thesealed end tubing walls. The resultant sintering, melting, anddistribution of the frit will adhere the expanded tube walls to oneanother and to its own sintered glass-ceramic mass to join the assembly20a into an integral unit and seal the spaces between and around theends of the tubes of the header connecting portions of the layers 30a,40a to prevent leakage of fluids from a header which is attached to theheader connecting tube portion assemblies.

There have thus been described a recuperator heat exchange assemblywhich comprises a plurality of layers of tubes having central tubeportions superimposed one above the other in successive parallel planesto form a stacked array. The central portions of the tubes within eachplane are essentially parallel to each other and to central tubeportions in the other planes. The central tube portions of part of thelayers form a first series of longitudinal passageways while theremaining central tube portions in the rest of the layers form a secondseries of longitudinal passageways. Each layer of first seriespassageways are in heat exchange relationship with at least one layer ofthe second series passageways. Each layer of tubes has header connectortube portions continuing outwardly from each end of each central tubeportion and away from the stacked array. The header connecting tubeportions have open ends for supplying fluid to and receiving fluid fromthe central tube portions.

The header connector tube portions of the first series of passagewaysdiverge from the header connector tube portions of the second series ofpassageways at each end of the central tube portions in the array, toseparate the sets of open tube ends thereof from each other to enableconnection of a separate header to each of the resulting four sets ofopen tube ends. In the embodiment illustrated in FIG. 13 the headerconnecting tube portions 36a and 48a diverge away from the axes of thestacked array of intermediate tube portions, while the header connectingtube portions 38a and 46a extend straight out from the stacked array ofintermediate tube portions. However, there is a relative divergencebetween the tube portions 46a, 36a and between the tube portions 38a and48a, even though the tube portions 46a and 38a are straight with respectto the axes of the intermediate tube portions 34a, 44a. Thus, the headerconnector tube portions will be described as diverging with respect toeach other, whether they are aligned with or oblique to the central tubeportions.

Header connecting means are provided for receiving each of the four setsof open tube ends, for supporting the tube ends and for closing thespaces between and around the open ends to prevent fluid leakage fromthe header between the header connecting tube portions.

The header connecting means illustrated in FIG. 13 includes a pluralityof tightly packed individually axially elongated elements, either tubesor rods or a mixture thereof, arranged with their axes parallel witheach other and in layers in the spaces between the header connector tubeportion layers. As shown in FIG. 13 the axes of the header connectorelements are also parallel with the axes of the header connector tubeportions of the layers 30a and 40a. However, it is to be understood,that the axes of the header connector elements may be arrangedtransverse to the header connector tube portions if the propercomposition and the proper amount of sealant is interposed in theinterstices between the header elements and the header connector tubeportions. Sealant means is interposed in the interstices between theheader connector elements, and between layers of header connectorelements and layers of header connector tube portions, to provide anonporous integral header connecting means in conjunction with theheader elements.

In the embodiment illustrated in FIG. 13 the axes of the intermediate orcentral tube portions 34a, 44a of each layer are aligned between theaxes of the intermediate tube portions of adjacent layers as illustratedin FIG. 8. Thus when the tubes are expanded the interstices between thetubes are more substantially filled or are substantially filled,depending upon the amount of expansion during heat treatment, and willresult in the substantially hexagonal cross-sectional areas asillustrated in FIG. 9 when the heat treatment is completed. Thesubstantially hexagonal configuration of FIG. 9 provides the mosteffective heat transfer efficiency.

Referring now to FIGS. 16 through 19 there are illustrated alternativeembodiments in a schematic form for building a structure, with separatedsets of open tube ends for connection to external headers, according tothe teachings of this invention. In FIG. 16 the tube 32b has anessentially straight central portion 34b and a header connector tubeportion 36b extending obliquely downwardly, while a header connectiontube portion 38b extends upwardly. A tube 42b has a central tube portion44b disposed in heat relationship with the central or intermediate tubeportion 34b and has a header connector tube portion 46b extendingupwardly, while the header connection tube portion 48b extends obliquelydownwardly.

In FIG. 17 the tube 32c has an intermediate portion 34c which issubstantially straight while the header connector tube portions 36c and38c extend straight outwardly from the intermediate tube portion 34c.The tube 42c has a substantially straight central portion 44c while theheader connecting tube portions 46c and 48c are diverged away from thetube portions 36c, 38c and obliquely away from the axes of both of theintermediate tube portions 44c, 34c.

In FIG. 18 the tube 32d has a straight intermediate portion 34d andagain has straight header connector portion tubes 36d, 38d extendingoutwardly from the ends of the intermediate portion 34d. The tube 42dhas a straight intermediate tube portion 44d, while the header connectortube portion 46d extends obliquely away from the intermediate portion44d in one direction and the header connector tube portion 48d extendsaway from the intermediate tube portion 44d in the other direction, toagain separate the tube ends into the four sets desired.

In describing the various embodiments of the invention therein there hasbeen disclosed a novel method for making the novel recuperator heatexchange assemblies which includes forming a multiplicity of elongatedtubes of a glass that is thermally crystallizable to a low expansionglass-ceramic. Each of the tubes have an essentially straight central orintermediate portion and header connector portions continuing from eachend of the central tube portion thereof. Each tube is filled with afluid medium that is expansible in response to the application of heatand the ends of the tubes are sealed to retain the expansible fluidmedium therein. The juncture of the header connector tube portions andthe central tube portions are heated and the header connector tubeportions of at least part of the multiplicity of tubes are bent withrespect to the central tube portions, so that first and second groups oftubes are formed in which the header connector portions of the twogroups diverge from each other when the central tube portions of tubesfrom each group are placed side by side or are stacked one above theother.

The tubes of the first and second groups are arranged into pluralitiesof layers with the central tube portions in each layer essentiallyparallel to each other. The plurality of layers of tubes aresuperimposed one above the other in successive parallel planes with thecentral tube portions of each layer essentially parallel to the centraltube portion of adjacent layers and with the layers of central tubeportions arranged next to each other in a stacked array. Each layer ofcentral tube portions of the first group are disposed in heat exchangerelationship with the layer of central tube portions of the secondgroup. The plurality of layers are arranged so that the header connectortube portions of the two groups diverge from each other at each end ofthe stacked array of central tube portions to provide four sets ofseparated header connector tube portion ends.

The spaces between and around the ends of each of the four sets ofseparated header connector tube portions are filled with a headerconnecting material that is thermally crystallizable to a low expansionglass-ceramic having substantially the same coefficient of linealthermal expansion as the elongated tubes. The outer surfaces of theassembly of the layers of tubes and header connector material areconstrained to restrict outward movement of the assembly.

The constrained assembly is subjected to a heat treatment which includestemperatures sufficient to soften the elongated tubes and to cause thefluid medium therein to expand to urge the tubes into contact with theadjacent tubes and the header connecting material to fuse the assemblyportions into an integral mass. The heat treatment further includestemperatures sufficient to effect crystallization of the tubes and theheader connector material into a low expansion glass-ceramic. The sealedends of the tubes are then opened to enable reception and discharge offluids therethrough for heat exchange therebetween.

The thermally crystallizable tubes have a wall thickness sufficient topermit substantially complete expansion of the stacked array of centraltube portions by the fluid medium therein during the heat treatment ofthe assembly. The central tube portions of one layer may be arrangedwith their axes in vertical planes extending through the lines ofcontact with tubes above and below, the tubes expanding to have asubstantially square or rectangular cross-section. The central tubeportions of one layer may also have their axes aligned between the axesof the corresponding tube portions in adjacent layers, the tubes thenexpanding to have a substantially hexagonal cross-section whichsubstantially fills all of the interstices between the central tubeportions.

There has thus been described novel heat exchange structures utilizingcounterflow techniques to obtain the most efficient heat exchange, whichhave no moving parts, and which have external header connections to aidin assembly of the structures to systems and which provide reducedturbulence in fluid flow through the structures.

There has also been described herein novel apparatus for making thetubular component layers of the novel heat exchange assembly.

A conveying means, which may include more than one conveyor as shown inFIGS. 10 and 11, is provided for receiving layers of tubular componentsand moving the layers through successive operation stations.

Means are provided for periodically depositing a plurality of elongatedtubes, in contiguous relationship with each other on the conveyingmeans, to form spaced pluralities of layers of tubes. Each of the tubesis deposited so that a central portion is supported by the conveyingmeans while at least one header connector portion extends outwardly fromthe supported central tube portion in a cantilevered arrangement withrespect to the conveying means.

A tube forming station is provided which includes means for heating eachtube at the junction of the central portion and at least one of theheader connector portions. Means are also provided at the formingstation for bending the heated tube to dispose the header connectorportion at a predetermined angle with respect to the central tubeportion. The bending means may include a conveyor edge portion formed toreceive and retain the bend of the header connector tube portion at thedesired angle as the force of gravity pulls the cantilevered headerconnector portion down on the conveyor edge portion. The conveyor edgeportion is formed at angle with respect to the horizontal portion of theupper flight of the conveyor.

Alternatively, for certain applications the tube bending means may alsoinclude means for mechanically engaging the header connector tubeportions, after the tube junctions have been heat softened, and movingthe header connecting tube portions to form the required predeterminedangle with the central tube portions.

Finally, means are provided for adhering or binding the tubes togetherin a layer to form an integral unit that may be easily handled.

The elongated tubes may be provided with their ends already sealed.However, if open-end tubes are deposited on the conveyor a tube sealingstation is provided which may include heating means for softening andsealing the open ends.

The apparatus also advantageously includes an aligning station locatedintermediate the tube forming and tube layer binding stations for movingthe bent header connector tube portions of a layer into a planarrelationship with respect to the central tube portions, with the headerconnector tube portions all extending in the same direction. In theembodiment disclosed herein the header connector tube portions areengaged by a second conveyor, as the layer moves along a guide ramp orslide, to move the header connector tube portions up into the planedefined by the central tube portions.

An overhead conveyor arrangement may be utilized to cooperate with thelayer conveying means to hold the tube layers in place while variousoperations are performed on the tube layers.

While there have been shown and described and pointed out thefundamental novel features of the invention with reference to thepreferred embodiments thereof, those skilled in the art will recognizethat various changes, substitutions, omissions and modifications in themethods and structures described may be made by those skilled in the artwithout departing from the spirit of the invention.

I claim:
 1. Apparatus for uniting oblique bent tubular components formaking heat exchange assemblies comprisinga constraining mold having abottom wall and integral opposed side walls, a pair of end wall members,means integral with the respective side walls for receiving the end wallmembers near the opposite ends thereof and detachably connecting saidend wall members in opposing relationship for selectively closing andopening the ends of the mold, said bottom and opposed side walls and endwall members connected thereon defining a cavity open at the top forreceiving an assembly of end bent tubular elements arranged in plurallayers, said cavity having an intermediate longitudinally extendingsection disposed parallel to said side walls and opposite oblique endsections for receiving said end bent tubular assemblies, each said endsection being contiguous with said intermediate section and disposedangularly with respect thereto, a top cover member adapted to close thetop of said cavity and thereby enclose the assembly of said tubularelements therein, said top cover member engaging and securing the endwall members along the adjacent edge thereof.
 2. The apparatus of claim1, which includes one or more perforations in said top cover member forconnecting the cavity to atmosphere for venting gases generated withinsaid cavity.
 3. The apparatus of claim 1, which includes one or moreperforations in said bottom wall for connecting the cavity to atmospherefor venting gases generated within said cavity.
 4. The apparatus ofclaim 1, wherein said means integral with the side walls for receivingthe end wall members comprise vertical opposed slots in the side wallsnear each of the ends thereof, and corresponding vertical ribs atopposite edges of each of said end wall members, said ribs adapted tonest in dovetail fashion in said slots, thereby detachably connectingsaid end wall members in opposing relationship for closing the ends ofthe mold.
 5. The apparatus of claim 1, wherein said opposite endsections of the said mold cavity are each angularly disposed withrespect to the longitudinal intermediate section thereof and flaredoutwardly therefrom, the extremities of said flared end sections of thecavity terminating at the said end wall members of the mold.